FIGS. 1A-1B depict a conventional nonvolatile logic device 10 formed using an array of magnetic junctions 12, 14, 16, 18, 20, 22, and 24. The junction 12 is an input magnetic junction 12. Also shown are an output magnetic junction 22 and intermediate junctions 14, 16, 18, and 20. A biasing junction 24 is also shown. However, an output electrode is coupled with the output magnetic junction 22.
The magnetic junctions 12, 14, 16, 18, 20, and 22 are typically tunneling magnetoresistive junctions. Thus, each junction 12, 14, 16, 18, 20, and 22 typically includes a pinning layer, a pinned layer, a nonmagnetic tunneling barrier layer, and a free layer. The pinned layer has its magnetization pinned in place by the pinning layer. The magnetizations of the free layers are shown in FIGS. 1A-1B and are typically free to move. The junctions 12, 14, 16, 18, 20, and 22 typically share a tunneling barrier layer, pinned layer, and pinning layer. Thus, the portions of the junctions 12, 14, 16, 18, 20, and 22 shown in FIGS. 1A-1B correspond to the free layer. As can be seen in FIG. 1A, the easy axis (corresponding to the shape anisotropy) for the free layer of the input magnetic junction 12 is perpendicular to the easy axes of the remaining magnetic junctions 14, 16, 18, 20, and 22. The remaining magnetic junctions 14, 16, 18, 20, and 22 are substantially identical. Thus, the magnetic junctions 14, 16, 18, 20, and 22, typically have the same shape anisotropy, magnetic moment, and other magnetic properties. The pinned layer typically has its magnetization oriented along the easy axis of the junctions 14, 16, 18, 20, and 22. Thus, the pinned layer is oriented perpendicular to the easy axis of the junction 12.
FIG. 1A depicts the nonvolatile logic device in a particular configuration. FIG. 1B depicts nonvolatile logic device 10 after switching to another configuration. The magnetic state of the input device 12 is changed, for example by passing the current through the structure causing spin transfer torque. An appropriate external magnetic field that saturates the magnetic junctions 14, 16, 18, 20, and 22 along their hard axes is applied. The result is that the magnetic moments of the junctions 14, 16, 18, 20, and 22 are aligned with the saturation field along the hard axis. As the external magnetic field is removed, the magnetic moment of the junctions 14, 16, 18, 20, and 22 cant away from the hard axis. For a situation in which the external magnetic field is removed at an appropriate time, the moments of the junctions 14, 16, 18, 20, and 22 would no longer be aligned in parallel. When the external field is completely removed, the state of the output junction will have switched because of the switch in the input junction, as is shown in FIG. 1B.
Although the conventional nonvolatile logic device 10 functions, there may be drawbacks. If an insufficient external field is applied, then the junctions 14. 16. 18, 20, and 22 do not saturate. The information in the input junction 12 may then not be transferred to the output junction 22. Alternatively, if too great an external magnetic field is applied, then the state of the input magnetic junction 12 may be changed. In addition, the time for which the external magnetic field is applied may be desired to be tightly controlled to ensure that switching is properly carried out. Thus, switching of the magnetic junction 11 may be unreliable and/or subject to tight tolerances.